U.S. patent application number 09/101306 was filed with the patent office on 2003-03-27 for three dimensional etching process.
Invention is credited to DEAN, ANTHONY B, DUTTON, DAVID T.
Application Number | 20030057177 09/101306 |
Document ID | / |
Family ID | 10786847 |
Filed Date | 2003-03-27 |
United States Patent
Application |
20030057177 |
Kind Code |
A1 |
DUTTON, DAVID T ; et
al. |
March 27, 2003 |
THREE DIMENSIONAL ETCHING PROCESS
Abstract
A method of forming three-dimensional structures on a substrate
by a single reactive ion each run whereby a mask is formed on said
substrate before a series of iterations are carried out, each
iteration including a mask etch and a substrate etch, so that
successive iterations give life to reduction in the mask area and
exposure of further areas of substrate.
Inventors: |
DUTTON, DAVID T;
(WORCESTERSHIRE, GB) ; DEAN, ANTHONY B;
(WORCESTERSHIRE, GB) |
Correspondence
Address: |
NIXON & VANDERHYE
1100 NORTH GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
222014714
|
Family ID: |
10786847 |
Appl. No.: |
09/101306 |
Filed: |
July 7, 1998 |
PCT Filed: |
January 9, 1997 |
PCT NO: |
PCT/GB97/00043 |
Current U.S.
Class: |
216/2 ; 216/11;
216/24; 216/26; 216/41; 216/49; 216/64; 216/67; 216/72; 216/74;
257/E21.038 |
Current CPC
Class: |
G03F 7/40 20130101; H01L
21/0337 20130101; G02B 3/0018 20130101; G03F 7/001 20130101; G02B
3/0012 20130101; G02B 3/0056 20130101 |
Class at
Publication: |
216/2 ; 216/26;
216/11; 216/24; 216/41; 216/49; 216/64; 216/67; 216/72; 216/74 |
International
Class: |
C23F 001/00; B44C
001/22; C03C 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 10, 1996 |
GB |
9600469.2 |
Jan 9, 1997 |
US |
PCT/GB97/00043 |
Claims
1. A method of producing or modifying a three dimensional surface
profile on a substrate comprising the steps of (i) forming a mask
of resist on the substrate such that some area of the substrate is
protected by the mask and some area is exposed and (ii) subjecting
the substrate and the mask to a plurality of iterations wherein
each iteration comprises at least one resist etch and at least one
substrate etch, the resist etch being carried out using a suitable
resist etchant, which modifies the shape of the mask and hence the
area of substrate exposed, and the substrate etch being carried out
using a suitable substrate etchant from which the mask affords
protection of the substrate, and which removes material from the
areas of substrate which are exposed, the resist etch and the
substrate etch being substantially asynchronous.
2. The method of claim 1 where an optical concentrator is formed in
the substrate.
3. The method of claim 1 or 2 where the substrate comprises a
semiconductor material.
4. The method of claim 3 where the substrate comprises InSb.
5. The method of claim 4 where the substrate etchant comprises a
CH.sub.4/H.sub.2 plasma.
6. The method of claim 5 where the resist etchant comprises an
oxygen plasma.
7. The method of claim 6 where a Winston cone emitter is formed in
InSb heterostructure material.
Description
[0001] The current invention relates to the production of three
dimensional structures on a substrate by Reactive-Ion Etching. It
can be applied to materials such as semiconductor, glass, polyimide
or any other which can be etched using a reactive ion plasma.
[0002] Three dimensional semiconductor structures are required for
optical confinement (for example in visible/infrared lenses,
emitters or detectors) and electromagnetic confinement (eg
microwave inductors, detectors or sources).
[0003] A number of techniques are known for the fabrication of
optical confining structures such as microlenses. For example,
Hutley et. al. teach the formation of small discs of photoresist
which, on heating to melt, are drawn into the shape of small lenses
by surface tension. (Physics World, July 1991 pp27-32).
[0004] Liau et. al. teach the formation of a stepped structure by
repeated applications of photolithography and bromine-methanol
etching. Mass transport within this structure to form a lens shape
is then effected, again by heating to melt (see Appl. Phys. Lett.
55 (2) 10 July 1989; The Lincoln Laboratory Journal, Volume 3,
Number 3, 1990). Other methods of forming microlens arrays are
detailed in "Micro-optics has macro potential" Laser Focus World
June, 1991. Methods which involve reactive ion etching typically
involve repeated applications of photoresist and etch runs. This
makes the fabrication process cumbersome.
[0005] According to this invention, a method of producing or
modifying a three dimensional surface profile on a substrate
comprises the steps of
[0006] (i) forming a mask of resist on the substrate such that some
area of the substrate is protected by the mask and some area is
exposed and
[0007] (ii) subjecting the substrate to a plurality of
iterations
[0008] wherein each iteration comprises at least one resist etch
and at least one substrate etch, the resist etch being carried out
using a suitable resist etchant, which modifies the shape of the
mask and hence the area of substrate exposed, and the substrate
etch being carried out using a suitable substrate etchant from
which the mask affords protection of the substrate, and which
removes material from the areas of substrate which are exposed.
[0009] In a preferred embodiment, an optical concentrator is formed
on the substrate.
[0010] In a preferred embodiment the substrate comprises a
semiconductor material.
[0011] In a preferred embodiment the substrate comprises InSb.
[0012] In a further preferred embodiment the substrate etchant
comprises a CH.sub.4/H.sub.2 plasma.
[0013] In a further preferred embodiment the resist etchant
comprises an oxygen plasma.
[0014] In a further preferred embodiment, a Winston cone is formed
in InSb heterostructure material.
[0015] The invention will now be described with reference to the
following figures in which FIGS. 1a-1e show representations of the
substrate and mask at various stages of a process using the method
of the current invention and
[0016] FIGS. 2a and 2b show scanning electron microscope images of
an array of microlenses during two stages of their formation by the
method of the current invention.
[0017] Referring to FIG. 1a, a dome or button of photolithographic
masking resist 1 is applied to a semiconductor substrate 2. This
may be formed by, for example, greyscale lithography (see UK patent
application 9310013.9) or resist-reflow methods.
[0018] The substrate is then etched using a substrate etchant from
which the resist 1 affords protection so that material is removed
from areas 3 on the substrate 2. This gives rise to the structure
shown in FIG. 1b.
[0019] Referring to FIG. 1c, the area covered by resist 1 is then
reduced, using a suitable resist etchant, so that further areas 4
of substrate 2 are exposed.
[0020] Further etching of the substrate using the substrate etchant
then removes material from areas 3 and 4 to produce a stepped
structure as shown in FIG. 1d.
[0021] Repeated etching of the resist 1 and substrate 2, in a
single reactive ion etch run, gives rise to the multi-stepped
structure shown in FIG. 1e.
[0022] Detailed three-dimensional structures can be formed by
controlling the rate and time for each of the etching steps. The
final resolution of the profile is dependent on the number of
alternate substrate and resist etch steps over a given structure
height.
[0023] This technique can also be used to modify structures formed
by other techniques.
[0024] Referring to FIGS. 2a and 2b, the microlenses shown therein
were fabricated using a Surface Technology Systems (STS) Reactive
Ion Etching Machine, Model 340PC, and the following etch
conditions:
1 Resist Etch conditions: Gas: O.sub.2, flow rate 80 standard cubic
centimetres per minute(sccm); Chamber Pressure: 60 mTorr; RF Power:
60 W. Substrate Etch Conditions: Gas: CH.sub.4, 90 sccm and
H.sub.2, flow rate 10 sccm; Chamber Pressure: 90 mTorr; RF Power:
50 W.
[0025] The substrate (InSb) was coated with 12.times.10.sup.4 m of
AZ4562 resist and was processed into straight sided cones using
greyscale technology and Ion beam milling. (Other methods of
effecting this part of the process will be apparent to those
skilled in the art). The sample was then resist etched using the
above resist etch conditions for 5 minutes. This was followed by a
5 minute InSb etch using the above substrate-etch conditions and
then another 5 minute resist etch. Four iterations of 5 minute InSb
etching and 2 minute resist etching were then performed to obtain
the structure shown in FIG. 2a.
[0026] A further seven steps resulted in the structure shown in
FIG. 2b.
[0027] Under some conditions, the exothermic nature of the reactive
ion etching process causes the resist to reflow. This gives
additional flexibility to the process and may obviate the need for
greyscale lithography or ex-situ resist reflow using, for example,
a hot plate or oven.
* * * * *